Technical Field
The present invention relates to a method for capturing a blade angle of a rotor blade of a rotor of a wind turbine. The present invention additionally relates to a measuring arrangement for capturing a blade angle of a rotor blade of a rotor of a wind turbine.
Description of the Related Art
The present invention is based, in particular, on a so-called horizontal-axis wind turbine having at least one, in particular three, adjustable rotor blades. These rotor blades can be adjusted in respect of their angle, and consequently their angle of attack, in relation to the wind, in order to extract from the wind a power that is as optimal as possible, or in order to reduce or limit the power extracted from the wind, in particular in the case of high wind speeds. In adjusting the angle of the rotor blade, which is also referred to as a pitching, the adjusting unit, in principle, can capture the current blade angle, which term is synonymous here with the term rotor-blade angle. This presupposes, however, that the actually existing rotor-blade angle is first equalized with the angle assumed by the adjusting unit. For this purpose, it is necessary to capture the actual rotor-blade angle, i.e., the actual position of the rotor blade. It might also be necessary to subsequently repeat or correct such an equalization.
In particular, it may happen that, in the case of three rotor blades, one is at an incorrect angle, namely, at an angle different from that of the other two rotor blades, and is therefore also at an angle different from that assumed by the adjusting unit. This angular variance is then persistently present, because the further adjustment of the rotor blades always starts from the incorrect angle, i.e., starts from one same angle for all three rotor blades, although one angle is different. Apart from a reduced efficiency because of the incorrect angle, this may also result in uneven loads on the rotor blades. As a result, in particular, any bearings are also subjected to asymmetric loading, in particular in respect of a rotation axis. Besides the unfavorable efficiency, therefore, there may be increased wear.
In connection with this, the German patent DE 100 323 14 C1, which also published as U.S. Pat. No. 7,052,232, proposes measurement of a distance between the tower of the wind turbine and a rotor blade rotating past the tower. In the case of this distance measurement by means of a laser distance sensor, the distance of the rotor blade as it rotates past, and consequently the contour of the rotor blade, is captured in a quasi-continuous manner. The laser distance measuring device is accordingly disposed on the tower, and can therefore perform this distance measurement and, consequently, can effect captures of the contour of the rotor blade as it rotates past.
The known profile and the captured contour of the rotor blade can then be used to determine the actual angle of the rotor blade. Such a measurement is performed for all rotor blades of the wind turbine, with no intermediate adjustment of the rotor blades being effected, such that all angles of these rotor blades can then be compared and adapted. This avoids the setting of differing blade angles.
In the case of this measurement, however, the angle captured by measurement of the distance is also influenced overall by the alignment of the wind turbine, namely, the so-called azimuth alignment of the wind turbine. If this alignment of the wind turbine, namely, in particular, the alignment of the nacelle of the wind turbine, which carries the rotor, or the alignment of the rotor axis, differs from the alignment of the laser distance sensor, that also alters the captured rotor-blade angle. However, the error that results from this is systematically the same for all rotor blades of the wind turbine, if the azimuth position remains unchanged during the measurement. Therefore, the rotor blades can thus nevertheless be equalized with each other.
Moreover, the patent describes that, in the case of a known angle between a laser beam and the hub, it is also possible to determine a “true” blade angle.
Such a determination of the angle between the hub and a measuring sensor can be difficult, however, at least if this measurement has to be highly accurate. Increased accuracy can be achieved for the measurement of the blade angle, i.e., for the measurement of the distance in relation to the blade, for the purpose of sampling the contour, by repeating the measurement, or measurements, of all rotor blades. This, however, only makes it possible to increase the accuracy of the blade angles of the rotor blades in relation to each other. In other words, in this case a relative blade angle can be captured, and only the accuracy of the latter can be increased. A relative blade angle is to be understood to mean the blade angle in relation to the other rotor blades. Capture of an absolute blade angle thus remains problematic, at least in respect of accuracy.
In the priority application relating to the present application, the German Patent and Trade Mark Office has searched the following prior art: DE 10 2011 053 968 A1.